X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.     

Isolation of humic acid from the brown algaPilayella littoralis

A standard humic acid extraction procedure has been used to isolate dark brown organic residues from samples of the macroscopic marine brown algaPilayella littoralis. The residues are insoluble in water, but soluble at high pH, and are similar in elemental composition, ash content, UV-visible, IR, PMR and X-Ray fluorescence spectra, X-Ray diffractograms and scanning electron micrographs to residues of a humic acid isolated from municipal compost. These results indicate thatPilayella produces humic acids.Author for correspondence     

Use of antibody/peptide constructs of direct antigenic peptides to T cells: evidence for T cell processing and presentation.

Human T cells can express MHC-class II products and were shown to be potential antigen-presenting cells. However, they are unable to capture the antigen and only antigens, which bind to T cell membranes such as the gp120 glycoprotein of HIV, are internalized, processed, and presented by T cells. To better understand the role of T cells as antigen-presenting cells, we established a method which overcomes the lack of antigen capture by T cells. Antigen (tetanus toxoid, TT) or an antigenic peptide of TT (residue 830-843, P2) was coupled to antibodies directed to T cell surface molecules such as CD2, CD4, CD8. Antibody/TT and antibody/P2 constructs stimulated P2-specific T cell clones in the absence of accessory cells, if the antibody recognized a T cell surface structure. Compared to the peptide alone, a 100-500 times lower molar concentration of the antibody/peptide construct was required to achieve a similar proliferative response. T cell stimulation via the constructs involved intracellular processing, as nonspecific, glutaraldehyde fixed T cell lines pulsed with the constructs could present the peptide and processing inhibitors like Leupeptin or Chloroquine inhibited the development of a proliferative response to the constructs. Our data underline the ability of T cells to function as antigen-processing and -presenting cells and show that antibody/antigen or antibody/peptide constructs are able to direct a certain antigen or peptide to a T cell. Antibody/peptide constructs may be interesting tools to better understand antigen processing and to study the consequences of antigen presentation by different cells.     

Evidence for Multiple, Local Functions of Ciliary Neurotrophic Factor (CNTF) in Retinal Development: Expression of CNTF and Its Receptor and In Vitro Effects on Target Cells

Abstract: There is increasing, although largely indirect, evidence that neurotrophic factors not only function as target-derived survival factors for projection neurons, but also act locally to regulate developmental processes. We studied the expression of ciliary neurotrophic factor (CNTF) and the CNTF-specific ligand-binding α-subunit of the CNTF receptor complex (CNTFRα) in the rat retina, a well-defined CNS model system, and CNTF effects on cultured retinal neurons. Both CNTF and CNTFRα (mRNA and protein) are expressed during phases of retinal neurogenesis and differentiation. Retina-specific Müller glia are immunocytochemically identified as the site of CNTF production and CNTFRα-expressing, distinct neuronal cell types as potential CNTF targets. Biological effects on corresponding neurons in culture further support the conclusion that locally supplied CNTF plays a regulatory role in the development of various retinal cell types including ganglion cells and interneurons.     

Altered surface glycoproteins in melanoma cell variants with reduced metastasizing capacity selected for resistance to wheat germ agglutinin

Variants of B 16-F 1 mouse melanoma cells selected for resistance to wheat germ agglutinin (WGA) toxicity $\text{in}\text{vitro}$ were found to have undergone a stable surface change correlated both to lectin resistance and reduced metastasizing potential. The surface alteration, as indicated by the increased electrophoretic mobilities of several lactoperoxidase-iodinated cell surface proteins in SDS-PAGE, was restricted to polypeptides able to interact with WGA. The availability of lectin-resistant melanoma cell variants having altered metastasizing behavior provides a promising approach to studies of the role of specific cell surface components in the metastasizing process.